Why were there such a huge discrepancies? This has not happened since 1988.

In 2016, the discrepancy between the popular votes for president and house was only 3.2%. In 2012, it was 2.7%. In 2008, it was 4.4%. In 2004, it was 0.2%. In 2000, it was 1%. In 1996, it was 8.5%. In 1992, it was 0.6%.

Nowadays it seems most voters give all of their votes to candidates from the same party (at least for federal elections). So it's hard for me to understand how 30-40 years ago large numbers of voters were splitting their votes. What changed? Why were voters so willing to split votes 30+ years ago but not today?

Small terminology nit-pick. You shouldn't use % to denote those discrepancies. The correct unit to use is percentage points.
– ArthurNov 8 at 14:04

I've taken out the bold emphasis. It seemed to be emphasising a great deal of pedantry.
– Mozibur UllahNov 8 at 14:32

@AndrewGrimm: It's actually rather fascinating, but the TL;DR is that the opposition candidate's campaign fell apart on the candidates own faults rather devestating. Ironically, nothing related to the Watergate Break-In sank the Democratic Ticket in '72.
– hszmvNov 8 at 22:49

3 Answers
3

Southern Democrats

In 1972, most southern states were overwhelmingly Democrat. But these Southern Democrats had a different ideology than Northern Democrats. They were more conservative, particularly on moral issues (e.g. sex outside marriage and abortion bad). Democratic presidential candidates tended to have Northern Democratic ideologies. As a result, Southern Democrats often voted for Republicans for president, but they would vote for other Southern Democrats for Congress.

In 1994, this changed. Southern Democrats increasingly voted Republican for Congress as well as the presidency. In fact, there is only one Southern Democrat left in Congress: Senator Joe Manchin from West Virginia.

Thanks Brythan, well said and certainly a factor. I almost used that word in my answer; remembering back to those times Southern Democrats churned up images of even older democrats dating back to the civil war. I remember electoral maps that were almost entirely red, not just the south.
– Burt_HarrisNov 8 at 1:26

14

@WesSayeed: The alignment “democrat = progressive, republican = conservative” wasn’t always established the way it is now, so as Southern Democrats saw it, Democrat politics were their particular kind of conservatism, and the Northern Democrats were the ones who were “not really Democrats”. Historically, the key differences between the parties have changed at various points, and the current alignment of democrats with progressive liberalism emerged (essentially) from the Northern Democrats “winning” the long factional battle with the Southern Democrats over the course of the 20th century.
– Peter LeFanu LumsdaineNov 8 at 9:26

4

@WesSayeed Though we all like to think we're freethinkers, statistically one of the most stable attributes a voter has is their partisan identification. When the mainstream Democratic party became more socially liberal, and the Republican party more socially conservative, people didnt just swap parties. The ones that did were mostly younger and more socially active. It takes big issues, like a presidential candidate, to make people to change their vote. The local candidates from the south were still just as conservative as the voters. The full shift took decades due to generational replacement
– TalNov 8 at 15:39

4

2010 is also important to note here. Here in TN, we still had quite a lot of Democrats up until 2010. My home congressional district (the home of Al Gore) had been blue almost without exception from reconstruction through 2010. Moderate Democrats pretty much stopped existing at the national level during Obama's first 2 years of office. Pelosi and Reid were forcing all Ds to back Obama's progressive agenda, which was very unpopular with the right-center districts represented by many moderate Democrats at that time. They all caved to Pelosi and they then all got voted out in 2010.
– reirabNov 8 at 17:32

1

Between 2004 and 2010, TN's Governor and both houses of its legislature also flipped blue to very solid red as the state Democratic Party leadership shifted to following the progressive wing of the party that was controlling the party in Washington instead of the moderate Democrats that had previously controlled TN politics.
– reirabNov 8 at 17:34

A lot of factors probably involved, for example the home states of presidential candidates and their running mates may have more influence over general election voting that strict party loyalty. Nixon and Reagan were from California, the state with the most electoral votes. Bush was from Texas, 2nd only to California in votes.

The 1984 electoral landslide is a strong example of this, with challenger Walter Mondale winning only his home state of Minnesota, and the perpetually Democratic District of Columbia.

For Ronald Reagan and George H. W. Bush I can get more specific. They had the support of a group of voters sometimes called the Reagan Democrats who voted a split-ticket. Some authors spoke of a Reagan Mandate, the phrase Peace thru Strength resonated. Reagan supporters and the country at large, seemed to share his desire to take a stronger line with the Soviet Union and favored spending more on national defense, which (perhaps counterintuitively) lead to reduction of tensions of the Cold War.

The premise of this question is incorrect. If you are touting statistics, please note that an event that is isolated such as a flip of a coin, you may conclude that any other flip has a 50/50 chance. Elections and power of an ideology is cyclical, and based on trends and the next cycle does not necessarily follow the results of the previous one. Liberal ideology as a political power is trending down and conservatism is trending up, just look at the number of elected liberal seats from the max in the 90s to now to see the trend
– Frank CedenoNov 8 at 15:55

@FrankCedeno I'm not sure where you're getting the idea that conservatism is trending up. Nationalism seems to be trending up and conservatism down (to take the UK and US examples in 2016, both Brexit and Trump were opposed by conservatives, and both Brexit and Trump were part of primarily nationalist movements).
– De NovoNov 8 at 23:23

A 50/50 split is also the natural state of a first-past-the-post election system: each political party adjusts its position to attract the majority of voters; since two parties are both doing this, the split tends to cycle around 50/50.
– MarkNov 8 at 23:55